# How much heat is lost through the roof and loft? > The 25% figure is for a roof with no insulation at all. Where it comes from, what UK sources say for an insulated loft, and what lofts here really have. Source: https://completeloftservices.co.uk/advice/how-much-heat-is-lost-through-the-roof/ Generated: 2026-11-02 --- - [Home](/) - [Advice](/advice/) - Heat lost through the roof Advice # How much heat is lost through the roof and loft? A home with no loft insulation loses around 25% of its heat through the roof, says the Energy Saving Trust. Insulation is what brings that down: in the government's model of the average UK home, heat lost through roofs fell by about two thirds from 1970 to 2011. A thin loft still loses more than it needs to, and more than 1 in 4 of the lofts measured here have under 150mm. ## Where does the 25% figure come from? From the Energy Saving Trust, and it is for a roof with no insulation at all. Its guide says: "Homes can lose around 25% of their heat through an uninsulated roof." It gives no source beside it. Most lofts here have some insulation. Fewer than 1 in 100 of the lofts measured (1,426 of 168,519) in our six councils are recorded with no insulation on their most recent certificate. A typical loft measured has 200mm. Sources: [Energy Saving Trust, roof and loft insulation](https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/), read 22 October 2026; [United Kingdom Housing Energy Fact File 2013](https://assets.publishing.service.gov.uk/media/5a75b123ed915d6faf2b4f5d/uk_housing_fact_file_2013.pdf), table 6n, read 22 October 2026. Source: our own count from government energy certificate data, explained on [how we work out our figures](/methodology/). Read October 2026. ## How much heat is lost through a loft that already has insulation? Much less, and that is down to insulation. The government's model of the average UK home put the roof at about 17% of heat lost in 1970, and about 8% by 2011. The government's fact file puts the fall down to lofts: "This reflects the dramatic improvement in loft insulation in new and existing homes." Those figures are modelled, cover all UK homes including flats, and stop in 2011. Locally, a typical loft measured has 200mm in every build era before 2003. That is short of the 270mm the Energy Saving Trust recommends. Sources: [Department of Energy and Climate Change, United Kingdom Housing Energy Fact File 2013](https://assets.publishing.service.gov.uk/media/5a75b123ed915d6faf2b4f5d/uk_housing_fact_file_2013.pdf), shares worked out from its table 6n, read 10 October 2026; our own count from government energy certificate data, explained on [how we work out our figures](/methodology/), read October 2026. ## Not sure how much is up there? Book a free survey and we will tell you what your loft has now. [Book a free survey](/contact/) ## How much difference does the first 100mm make? Most of it. A thin loft is where a top up does the most work. Energy assessors give a bare loft a U-value of 2.3. Lower means less heat lost. 100mm takes it to 0.40, and 270mm to 0.16. More than 1 in 4 of the lofts measured here have under 150mm: 44,606 of 168,519. [The full table, and 270mm against 300mm](/advice/270mm-vs-300mm-loft-insulation/). Sources: [BRE, RdSAP 10 specification](https://bregroup.com/documents/d/bre-group/rdsap-10-specification-10-06-2025), table 16, read 8 October 2026; our own count from government energy certificate data, explained on [how we work out our figures](/methodology/), read October 2026. ## How can I tell if heat is escaping through my loft? Start with your energy certificate, then look in the loft. Our [loft checker](/tools/epc-loft-checker/) shows the depth recorded on your certificate. Then check what is really up there. If you live in South Cambridgeshire, the council says you can borrow a thermal camera through a local charity scheme. It says the camera "can usually be used between around November and the end of March", because "There needs to be around 10 degrees difference in temperature between the outside and the inside, for the camera to show heat loss effectively." Source: [South Cambridgeshire District Council, thermal imaging cameras](https://www.scambs.gov.uk/climate-and-environment/energy-saving/thermal-imaging-cameras). Read 22 October 2026. ## Short answers **How do you stop heat escaping through the roof?** Bring the loft insulation up to depth and keep it fluffed up. [The Energy Saving Trust](https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/) recommends at least 270mm of mineral wool, one layer between the joists and a second across them, and warns not to squash it. So boards go on raised legs above it. The hatch counts too: [should a loft hatch be insulated?](/advice/should-a-loft-hatch-be-insulated/) We [insulate lofts](/loft-insulation/) to 270mm and fit boards on raised legs, so you can store things without losing the warmth. **Which part of a house loses the most heat?** The walls. [The Energy Saving Trust](https://energysavingtrust.org.uk/energy-at-home/reducing-home-heat-loss/) says a typical uninsulated home loses about a third of its heat through the walls and about a quarter through the roof. In the government's model of the average UK home in 2011, walls were about 33% of the heat lost and the roof about 8%. **Does loft insulation cut bills by 25%?** That is not what the figure means. The 25% is the Energy Saving Trust's share of heat lost through a roof with no insulation at all. It is a share of heat, not of your bill. **Does a bungalow lose more heat through the roof?** The Energy Saving Trust's model puts the carbon saved by insulating a bare bungalow loft at 1,100kg a year. That is close to a detached house at 1,200kg, and nearly double a semi at 600kg. Bungalows here tend to be better insulated, though. A typical bungalow loft measured has 250mm, against 200mm for houses. Fewer than 1 in 5 bungalow lofts measured have under 150mm (17.4%). For houses it is more than 1 in 4 (28.4%). **What are the downsides of loft insulation?** It makes the loft itself colder, so pipes and tanks up there need insulating too. The Energy Saving Trust also says condensation becomes more likely if the loft is not ventilated. [Will loft boarding cause condensation?](/advice/will-loft-boarding-cause-condensation/) Sources: [Energy Saving Trust, roof and loft insulation](https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/), read 22 October 2026; [Energy Saving Trust, reducing home heat loss](https://energysavingtrust.org.uk/energy-at-home/reducing-home-heat-loss/), read 10 October 2026; [United Kingdom Housing Energy Fact File 2013](https://assets.publishing.service.gov.uk/media/5a75b123ed915d6faf2b4f5d/uk_housing_fact_file_2013.pdf), table 6n; our own count from government energy certificate data, explained on [how we work out our figures](/methodology/), read October 2026. ## More advice - [270mm or 300mm: is deeper worth it? What each depth does, in the assessors' own figures.](/advice/270mm-vs-300mm-loft-insulation/) - [How much loft insulation do I need? 270mm, where that comes from, and what lofts here have.](/advice/how-much-loft-insulation-do-i-need/) - [Top up old insulation or replace it? Condition decides it, not age.](/advice/top-up-or-replace-old-insulation/) [All loft advice](/advice/) ## Find out what your loft has now The quarter is for a bare roof. What matters for your home is how much is up there now, and a thin loft is where a top up does the most. Check what your certificate says, then book a survey. We [insulate lofts](/loft-insulation/) to 270mm, and we can [board and insulate](/loft-boarding-and-insulation/) together. The survey is free and takes about twenty minutes. You get a written price before any work starts. [Book a free survey](/contact/) [Loft insulation](/loft-insulation/) Complete Loft Services sorts out loft boarding and insulation across Cambridgeshire and the surrounding counties. Complete Loft Services sorts out loft boarding and insulation across Cambridgeshire and the surrounding counties. The survey is free, and you get a written price before any work starts. Written by Ben Criddle, who runs Complete Loft Services. Published 26 October 2026 . Facts checked on 10 October 2026 .